1. Field of the Invention
The invention generally relates to an optical transmission module, and in particular relates to an optical transmission module using a flexible printed circuit board as a connecting interface between the photoelectric element and the circuit board.
2. Related Art
In the field of optical data processing, optical transmitter/receiver transmits the data signal of processed information through an emitter into optical signal. The optical signal transferred through optical fiber to a remote photoelectric receiver where the optical signal is further converted into electrical signal so as to accomplish data communication.
Some prior art optical data transmission modules are disclosed in patents such as U.S. Pat. No. 5,742,480 and U.S. Pat. No. 5,513,073.
In U.S. Pat. No. 5,742,480, a flexible printed circuit board is used to carry the circuit of whole module. The integrated circuit element is soldered directly on the flexible printed circuit board. The complicated control circuit and photoelectric element are all mounted on the board. The photoelectric element is fixed on the board through holes. In order to align the optical axis, an almost right angle bend for the flexible printed circuit board is required.
In U.S. Pat. No. 5,513,073, an optical transmission module mainly includes a flexible printed circuit board, heat spreader and thermal isolator. The flexible integrated circuit is similar to U.S. Pat. No. 5,742,480 that a complicated control circuit and photoelectric element is used; holes and almost a right angle bend are required for optical axis alignment.
The U.S. Pat. No. 5,742,480 and U.S. Pat. No. 5,513,073 have some possible problems. For example, the multiple-layer flexible board used in U.S. Pat. No. 5,742,480 increases the manufacturing difficulty. The circuits on the flexible board of the two patents are very complicated that make the fabrication and assembly difficult. The connections between the optical members and the flexible printed circuit board require holes that easily cause signal distortion, parasitic effects and fail to achieve high data rate transmission. Further, the bending of the flexible printed circuit board easily causes unreliable signal. The signals at the transmitter and the receiver are easy to be influenced. No countermeasures are provided in the prior arts.
Another prior art of optical transmission module is illustrated in FIG. 1. The photoelectric element 10 has a signal pin 11 and a non-signal pin 12 connecting to the integrated circuit 40 on the main circuit board 30 via connecting points 60 and transmission lines 41, 42. The photoelectric element 20 has a signal pin 21 and a non-signal pin 22 connecting to the integrated circuit 50 on the main circuit board 30 via connecting points 60 and transmission lines 51, 52. The connectors in this construction have problems of stress during connecting and decrease signal fidelity and cause interference to the receiver.
As described above, the optical transmission modules of prior arts have problems of lower signal fidelity and interference between transmitter and receiver.